Thx to Alwyn Cutmore for helping me, I was able to refine my research
on whether our Atlas B40-8 mechansim with C628 trucks gives or doesn't give accurate
RSD-15 wheelbase.
Bottom line:
**We are back to original conclusion
**Atlas B40-8 mechanism with Atlas C628 trucks gives accurate RSD-15 wheelbase
Whew!
Thx to Alwyn for helping so much for this research. Our rivet counting conscience can now go and
build massive numbers of RSD-15's in peace, using this combination of mechanism and trucks.
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For those who care, below I've included the calculation, combining data from the following sources:
* Data in the
http://hosam websites for the Alco Roadswitcher dimensions:
http://www.hosam.com/alco/rsdim.html* Same website, GE B40-8 truck center to center wheelbase dimensions:
http://www.hosam.com/ge/gewhb.html* RSD-15 plans
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Here's the computation. By looking at the RSD-15 plans:
* The Alco RSD-15 plans show center to center of Alco trimount trucks TRUCK BOLSTERS is 43'-06" (confirming Note 2 in the HOSAM table).
* However, the plans also CLARIFY that distance, by identifying this location is 1' 10" OUTBOARD of the center axle
(the plans/pictures worth 1000 words, from the plans, now I realize what the HOSAM table was trying to say)
* In other words, the Alco trimount truck's CENTER AXLE is therefore 1'-10" INBOARD of the TRUCK BOLSTER
* Remembering that the gear tower of the N scale Atlas C628 trucks is directly over the center axle.....
* We therefore need to calculate the prototype RSD-15's center-axle to center-axle distance
* To do that, we calculate: (RSD-15 TRUCK BOLSTER distance) - (1' 10" front truck) - (1' 10" rear truck)
* Plugging in the numbers: (43' 6") - (1' 10") - (1' 10") =
* And that equals 39' 10" distance center-axle to center-axle
* I used my N scale-ruler to measure my B40-8 chassis with C628 trucks
* It measures exactly spot on that distance - COOL!!!
So, next I investigated why the Atlas B40-8 mechanism + C628 trucks gives this accurate wheelbase.
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To do that, I researched the GE B40-8 center-of-truck to center-of-truck distance, to compare this to the Alco 39' 10" distance
* We see from:
http://www.hosam.com/ge/gewhb.html * That the GE Dash 8-40 truck center-center distance is 39' 0"
* And that's only 10" off from the Alco RSD-15 center-axle-center-axle spacing is 39' 10"
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* We can see from following photos, the B40-8 truck gear is centered on the 39' mark per B40-8 dimensions
* We can see the C628's gear tower is over the center axle, therefore in a B40-8 mechanism, the center axles would be.... 39' feet apart
http://www.pbase.com/atsf_arizona/image/148672764-----------------------------------
What this means is the Atlas B40-8 mechanism locates the C628 gear towers a scale 39' apart
Which is within 10" of what a perfect scale gear tower location of the Atlas C628/C630 trucks should be for an RSD-15
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This happy circumstance happens because the Atlas N scale C628 truck gear tower is centered over the middle axle,
NOT over the actual middle of the truck.
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Whew!
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All this is why the Atlas N scale B40-8 mechanism turns out to be a almost perfect spot on match
for correct RSD-15 truck spacing, using the Atlas C628 / C630 trucks
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If this is how SSWJIM (Jim Bence, San Diego Society of N Scale) figured out that the Atlas B40-8 mechanism with Atlas C628 trucks combination
is the best fit for under the MRC RSD-15 shell, my hat's off to him, he's a smarter man than I am.
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As I said in beginning, thx to Alwyn Cutmore for helping so much for this research.
Our rivet counting conscience can now peacefully go and kitbash, massive numbers of RSD-15's using MRC shells,
over mechanisms that are combination of N scale Atlas B40-8 mechanism and Atlas C628/C630 trucks.
